Influence of an Increased Case Hardening Depth on the Tooth Root Load Carrying Capacity of Large Modulus Cylindrical Gears Made of Materials with Higher Hardenability*

Abstract Highly stressed gears are usually manufactured from case hardening steels. The case hardening depth (CHD) has a significant influence on the tooth root load carrying capacity. For the materials 16MnCr5 and 20MnCr5, comprehensive investigations have been carried out in the past to determine the optimum case hardening depth up to size module mn = 10 mm on cylindrical spur gears. In certain applications, however, it may be necessary to select an increased CHD, e. g. to reduce the risk of tooth flank breakage. The question therefore arises as to what extent the available findings on the influence of the CHD on the tooth root load carrying capacity can also be transferred to materials of higher hardenability and larger sizes. For this purpose, several materials with different alloy systems and hardenabilities were examined under variation of the case hardening depth. In addition to extensive material characterization, pulsator tests were carried out to determine the tooth root load-carrying capacity on test gears of size mn = 12 mm. It is shown that the results obtained on MnCr steels up to size mn = 10 mm can in principle also be transferred to the variants investigated here.